This invention relates to novel proteins and genes coding the same, more specifically to protein NMDA (N-methyl-D-aspartic acid) type glutamate receptors which play a central role in nervous information transmission, modified products thereof, and genes (cDNAs) encoding them.
It has been suggested that glutamate receptors, which are receptors of main stimulant nervous transmitter substances in a central nervous system of a higher animal, play a central role in nervous information transmission at a synapse, and also are deeply concerned with appearance of synapse plasticity which is basically required for memory and learning and neuronal cell death caused by a disease such as cerebral ischemia and epilepsy. Thus, it is considered that clarifications of molecular structures and functions of the glutamate receptors are required to understand a transmission mechanism of nervous information in a center, a cerebral structure of higher order and the disease of a brain.
As in the case of receptors of acetylcholine and GABA (.gamma.-aminobutyric acid), the glutamate receptors are roughly classified into ion channel type glutamate receptors and G protein coupled type receptors (metabolism-controlling type receptors). Receptors which can effect long-term reinforcement of synapse transmission at a CA1 region of a hippocampus of which the most advanced study has been made about synapse plasticity are two kinds of ion channel type glutamate receptors. That is, an NMDA type receptor having Ca.sup.2+ permeability and opening depending on membrane potential and a quisqualate/kinate type receptor (or a non-NMDA type receptor). While the non-NMDA type receptor performs general synapse transmission, the NMDA type receptor performs Ca.sup.2+ permeation when a high frequent. stimulus which induces long-term reinforcement of synapse transmission is given. The Ca.sup.2+ permeation is inhibited by Mg.sup.2+ depending on membrane potential.
Although the glutamate receptors have important physiological functions as described above, molecular biological structures thereof had not been clarified for a long term. In recent years, by using a cDNA-producing system of Xenopus oocytes, Hollmann et al. cloned cDNA of a non-NMDA type glutamate receptor ("Nature", 342, pp. 643 to 648 (1989)) and Nakanishi et al. cloned cDNA of a rat-G protein coupled type glutamate receptor ("Nature", 349, pp. 760 to 765 (1991)) and cDNA of a rat-NMDA type receptor ("Nature", 354, pp. 31 to 37 (1991)). Other plural kinds of genes of glutamate receptors have been cloned, and the molecular biological mechanisms thereof have not yet been clarified sufficiently under the present situation.